1. Field of the Invention
The present invention relates to a head mounted display (HMD) which is capable of implementing a high-magnification image using a secondary image forming system and which uses a single display unit, and an optical system for use in the HMD, which can allow an image provided by a small-sized display device of 0.7 inch or less to be viewed in an enlarged scale of angular magnification of substantially 10 times.
2. Description of the Related Art
In general, a head mounted display (referred to as HMD hereinafter) forms an image using a display device such as a liquid crystal display device (LCD) and enlarges the formed image using a mirror to be viewed in an enlarged scale. The HMD is used in the state where it is mounted on the head of a viewer.
Referring to FIG. 1, a conventional HMD includes a back light source 11, an image generating means 15 for generating an image by selectively transmitting light irradiated from the back light source 11, a spherical reflecting mirror 19, and a half mirror 17 for reflecting the light having passed through the image generating means 15 toward the spherical reflecting mirror 19 and transmitting the light reflected from the spherical reflecting mirror 19 to a viewer""s eye 24.
The HMD having the aforementioned configuration is installed in a housing 20 constructed to be mounted on the head of a viewer. The light reflected from the spherical reflecting mirror 19 and having passed through the half mirror 17 is directed to the viewer""s eye 24 through a window 22.
The back light source 11 includes a lamp 12 which is a luminous body such as a fluorescent lamp, and a mirror 13 installed on one surface of the lamp 12 to make the light irradiated from the lamp 12 travel in one direction. The image generating means 15 includes a transmission type LCD 16 having two-dimensional pixels and which is independently driven in units of each pixel, and a pair of polarizers 17a and 17b installed in the front and rear of the LCD 16. The conventional HMD includes a pair of optical systems having the configuration shown in FIG. 1 to be used for viewer""s left and right eyes, respectively.
The magnification of the HMD, that is, angular magnification, is determined by curvature of radius of the spherical reflecting mirror 19. Here, the angular magnification is defined by Expression (1) represented by a focal length fxe2x80x2 of the spherical reflecting mirror 19 and a distance of distinct vision (which equal 250 mm) to indicate the enlargement capability of an HMD.                               Angular          ⁢                      xe2x80x83                    ⁢          magnification                =                              Distance            ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            distinct            ⁢                          xe2x80x83                        ⁢            vision                                f            xe2x80x2                                              (        1        )            
As described above, according to the conventional HMD, it is quite difficult to achieve angular magnification of over 10 times. In order to increase the angular magnification, since the curvature of radius of the spherical reflecting mirror 19 must be made small, the focal length of the spherical reflecting mirror is reduced. Thus, the LCD 16 must be disposed close to the half mirror 17. However, if the LCD 16 is close to the half mirror 17, the optical path may be shielded. Thus, it is difficult to attain high magnification of over 10 times. Also, since a pair of LCDs are used, the cost is high.
To solve the above problems, it is an objective of the present invention to provide a head mounted display (HMD) which generates an image using a single image generating unit of a small display device and is capable of implementing a large screen, and an optical system for use in the HMD.
Accordingly, to achieve the above objective, there is provided a head mounted display device including: a light source for generating and irradiating light, image generating means for generating an image from light irradiated from the light source, an image forming lens unit for primarily forming the image generated by the image generating means, first light branching means for transmitting and reflecting the image generated by the image generating means and branching the image, first light path converting means for converting the traveling path of the image reflected from the first light branching means, a first reflecting mirror on which the image is received from the first light path converting means is reflected toward an eye of a user, second light branching means disposed on the light path between the first light path converting means and the first reflecting mirror, for changing the traveling path of the incident image, second light path converting means for converting the traveling path of the image having passed through the first light branching means, a second reflecting mirror on which the image received from the second light path converting means is reflected toward the other eye of a user, and third light branching means disposed along the light path between the second light path converting means and the second reflecting mirror, for changing the traveling path of the incident image.
According to another aspect of the present invention, there is provided an optical system for a head mounted display device for forming an image which is generated by a display device, by enlarging the image using light irradiated from a light source. The optical system includes an image forming lens unit, for focusing the image generated by the display device, having at least one lens made of a material having a high refractive index and a high dispersion in order to have a strongly negative power, and at least one lens made of a material having a low refractive index and a low dispersion in order to have a strongly positive power. The optical system further includes a field lens, having a positive power, for forming the focused image on a primary image forming plane, a semi-transmissive mirror for transmitting or reflecting incident light to change the traveling path of the incident light, and a reflecting mirror, on which the incident light branched from the semi-transmissive mirror lands, for reflecting the light toward an eye of a user to allow the light to be directed toward the pupil of the user.